refactor: rework nix flake

Co-authored-by: Amaan Qureshi <amaanq12@gmail.com>

docs/flake.nix

@@ -1,38 +0,0 @@
-{
-  perSystem =
-    {
-      pkgs,
-      lib,
-      src,
-      version,
-      ...
-    }:
-    {
-      packages.docs = pkgs.stdenv.mkDerivation {
-        inherit src version;
-
-        pname = "tree-sitter-docs";
-
-        nativeBuildInputs = [
-          pkgs.mdbook
-          pkgs.mdbook-admonish
-        ];
-
-        buildPhase = ''
-          cd docs
-          mdbook build
-        '';
-
-        installPhase = ''
-          mkdir -p $out/share/doc
-          cp -r book $out/share/doc/tree-sitter
-        '';
-
-        meta = {
-          description = "Tree-sitter documentation";
-          homepage = "https://tree-sitter.github.io/tree-sitter";
-          license = lib.licenses.mit;
-        };
-      };
-    };
-}

docs/package.nix

@@ -0,0 +1,33 @@
+{
+  stdenv,
+  lib,
+  version,
+  mdbook,
+  mdbook-admonish,
+}:
+stdenv.mkDerivation {
+  inherit version;
+
+  src = ./.;
+  pname = "tree-sitter-docs";
+
+  nativeBuildInputs = [
+    mdbook
+    mdbook-admonish
+  ];
+
+  buildPhase = ''
+    mdbook build
+  '';
+
+  installPhase = ''
+    mkdir -p $out/share/doc
+    cp -r book $out/share/doc/tree-sitter
+  '';
+
+  meta = {
+    description = "Tree-sitter documentation";
+    homepage = "https://tree-sitter.github.io/tree-sitter";
+    license = lib.licenses.mit;
+  };
+}